The spinal column is a flexible chain of closely linked vertebral bodies. In a normal human spine, there are seven cervical, twelve thoracic and five lumbar vertebrae. Below the lumbar vertebrae are the sacrum and coccyx. Each individual vertebral body has an outer shell of hard, dense bone. Inside the vertebral body is a honeycomb of cancellous bone containing red bone marrow. All of the red blood cells, and many of the white blood cells, are generated inside the cancellous bone where the blood cells mature before being released into the blood stream.
The intervertebral disc, also known as the spinal disc, serves as a cushion between adjacent vertebral bodies so as to permit controlled motion therebetween. A healthy intervertebral disc consists of three components: a gelatinous inner core (the nucleus pulposus), a series of overlapping and laminated plies of tough fibrous rings (the annulus fibrosus), and superior and inferior thin cartilage layers connecting the intervertebral disc to the thin cortical bone of the adjacent vertebral bodies (the vertebtral end plates).
An intervertebral disc may be displaced and/or damaged due to trauma (e.g., a herniated disc) or by disease (e.g., a degenerative disc disease). A herniated disc may bulge out and compress itself onto a nerve, thereby resulting in lower leg pain, loss of muscle control or paralysis. To treat a herniated disc, the offending portions of the disc, which typically includes a bulging portion of the nucleus pulposus, are removed via well-known surgical procedures. A degenerative disc disease typically causes the intervertebral disc to gradually reduce in height, thereby causing the annulus fibrosus to buckle, tear or separate in a radial and/or circumferential direction, commonly resulting in persistent and disabling back pain. Degenerative disc disease may be treated by surgically removing the nucleus pulposus and fusing the adjacent vertebral bodies to stabilize the joint. In either case, whether removing some or all of the nucleus pulposus, these procedures place greater stress on adjacent intervertebral discs to compensate for lost motion capabilities which may in turn cause premature degeneration of the adjacent intervertebral discs.
One drawback of current prosthetic disc implants is that the annulus fibrosis and/or other portions of the intervertebral disc are weakened by either large or multiple incisions and/or cut outs that are required in order to insert the prosthetic disc implant into the intervertebral space between adjacent vertebrae. Additionally, incisions or cut outs in the annulus fibrosis are not easily repaired, thereby increasing the risk that the prosthetic disc implant may eventually work its way out of the intervertebral space and possibly interfere with or damage adjacent anatomical tissue. A further deficiency of current prosthetic disc implants is that multiple laterally spaced prosthetic implants are sometimes required to be inserted within the intervertebral space, thereby requiring careful and precise positioning of the prosthetic implants to ensure proper load carrying characteristics. (See, e.g., U.S. Pat. No. 5,674,295 to Ray et al.).
Modern trends in surgery are directed toward restoration of bodily function and/or form (i.e., repair) of anatomical structures through the use of minimally invasive surgical techniques. The ability to surgically repair damaged tissues or joints via the creation of a minimal number of incisions and as small incisions as possible produces less trauma and pain for the patient while generally yielding better clinical outcomes.
Thus, there is a general need in the industry to provide improved instrumentation and methods for delivering an implant into a vertebral space, preferably in a minimally invasive manner. The present invention meets this need and provides other benefits and advantages in a novel and unobvious manner.